For those that are familiar and comfortable using hand held trim routers, down spiral flush cutting bits offer a quick process for this operation. Shear cutting trim bits would be the second choice with a router. Straight flush cutting laminate trim bit can be used but are a little risky because tear out is likely.

The process described below is recommended, while not as fast as the router, the procedure will produce professional results.

Trimming the Top or Back Edges -- Flapper wheel method

I found that an abrasive 80-grit flapper wheel (Sears and others) works well for trimming the tops or back flush to the rim. This procedure is less aggressive than a router with a flush cutting bit. However care must be taken to avoid tear out. The areas indicated by the blue tape are the most vulnerable. Sometimes the top or back is not in perfect contact with the rim and kerfing. Consequently, the combination of end grain and a poor glue joint can cause a problem.

The rim must be secure and stable. Also cover the top or back with a piece of cardboard, there is a chance that you will bounce off the edge and this could damage the top or back.

Trim the precautionary areas first, tilt the drill and flapper wheel in such a way that it is sanding/trimming in a slightly downward angle to the face of the top or back.

I think you will find that this process is much less intimidating than whacking at your newborn guitar body with a high-powered router. You may need to do a little hand sanding; this is necessary even with the router procedure. Work slowly to prevent damage to the rim. Still this method is much quicker and more accurate than hand tools.